Chemical Concepts
(Back to Radiometric Dating Home) Oftentimes, the people who need radiometric dating the most and the people who understand radiometric dating the most are not the same people. Radiometric dating is a fairly advanced chemical technique and requires a decent amount of background knowledge. However, it is hard to acquire this knowledge quickly and easily. This page will describe several aspects of the chemical background that will assist in the understanding of Radiometric Dating. __TOC__ Structure of the Atom Almost everything in the Universe is comprised of matter. While matter has several slightly different definitions, for the purposes of this discussion it can just be thought of as what makes up all physical objects. All matter is made up of small particles called atoms. An atom has three major parts: protons, neutrons and electrons. Protons and neutrons cluster towards the center of the atom, while electrons orbit it. In order to better understand atoms the concept of elements can be applied. Elements provide a system of classification for all the different types of atoms. Each atom is named based on its number of protons, for instance, every atom that has only one proton is an atom of Hydrogen by definition. By the same rules, any atom that contains exactly eight protons is identified as an atom of Oxygen. Charge is a rationalization of how subatomic particles interact. The rules are thus: opposite charges will attract and like charges will repel. Protons have a charge of +1, neutrons are 0, and electrons are -1. This attraction explains the orbital movement of electrons. Protons and neutrons are large and cluster in the center of an atom (an area that is referred to as the nucleus). Therefore the nucleus has a positive charge (only the protons contribute). http://www.epa.gov/radiation/understand/atom.html Isotopes An atom of Carbon always has six protons—that is a fact. However, its number of neutrons and electrons is not defined by its elemental name. There are several different versions of each element with different numbers of neutrons; these are referred to as isotopes. Atoms that don’t have the same number of electrons and protons are referred to as ions. For instance, the most common isotope of Hydrogen contains one proton, no neutrons, and one electron. This isotope is referred to as Protium because its nucleus consists of only one proton. There exist atoms that have one proton, one neutron, and one electron. These atoms are of the element Hydrogen based on their proton number, but they are of a different isotope: Deuterium. These isotopes are comparably stable, but Protium is far more abundant than Deuterium. Radioactivity and Decay There exists a third isotope of Hydrogen; however this isotope behaves significantly different than the other two. Tritium (containing two neutrons), is not stable under normal conditions. If left alone it will emit Beta particles (very similar to electrons) and the resulting atoms will contain two protons and a neutron in its nucleus. This phenomenon is known as radioactive decay (it is called this because particles are radiated from the parent, and a different atom remains at the end). There are many radioactive isotopes in existence and there are several types of decay. The principles of radioactive decay are clear and constant in every case. A radioactive element emits some sort of particle or energy, and becomes a different element or isotope. Every isotope has what is known as a half-life. A half-life is the time it takes for exactly one half of a sample to decay completely. A half-life is a core property of an isotope. It will take twelve years for one half of a sample of Tritium to decay, and it will take an additional twelve years for one half of the remaining sample to decay. A 2g sample will take twelve years to decay to 1g, and that sample will take twelve years to decay to 0.5g. http://www.epa.gov/radiation/understand/atom.html References ::#US EPA | What is an atom? (2010, February 23). Retrieved from: http://www.epa.gov/radiation/understand/atom.html ::#US EPA | Why are some atoms radioactive? (2010, February 23). Retrieved from http://www.epa.gov/radiation/understand/radiation.html